[RTLUNT]

During washer installation, I installed a Hot/Cold water/Drain connection unit in the washer room. The Drain connection pipe plug fell down the drain pipe. The drain trap is located within the washer room wall about washer base level. How do I remove remove the pipe plug without cutting a hole in the wall to gain access to the trap?

[speedball1]

How do I remove remove the pipe plug without cutting a hole in the wall to gain access to the trap?

If I understand you correctly you installed a washer box,(see image) and the knockout fell down the stand pipe into the trap. Right?
This will be a toughie! Can you shine a light down there and tell me how the plug's laying in the trap? Is it crossways or edge up? If it were crossways I'd rent a 3/8ths." power snake and take my bench grinder to grind a real sharp end on the tip of the auger. I would then attempt to auger into it and drag it back out.
If it's on edge I'd take a stiff wire and load it up with some of that sticky stuff they put on a pad to trap roaches and see if I could drag it back that way.
But let's be realistic! Chances are you'll end up cutting a square hole ,(you'll use it later for a patch) in the wall, cutting the stand pipe a inch or so above the trap and fishing that sucker out of there, To couple back it would be easier to use a shielded Metal coupling, (see image) then to prime and glue in a plastic coupling. Good luck and happy fishing. Tom